Study On Technology Of Preparing Of Multicrystalline Silicon Texture Surface

Surface texturing is one important way to improve the photoelectric conversionefficiency of the multicrystalline silicon solar cells, because of reducing the loss of lightof surface reflection in the solar cell. After the surface treatment, the silicon surfaceshowing the hole-like form and uneven surface, which may reduce the reflection andincrease visible light absorption of surface, and improve the conversion efficiency of thesolar cells, finally.In this paper, the electrochemical pre-etching technology and optical mask methodare respectively used with the traditional chemical acid etching technology, to improvethe multicrystalline silicon texture surface, and increase the conversion efficiency ofmulticrystalline silicon solar cells.1) The chemical acid etch reaction of the multicrystalline silicon texture surface isstudied in HF/HNO₃mixed solution system. The composition and ratio of the corrosionsolution, the corrosion reaction time and the corrosion reaction temperature of theimpact factors of chemical acid etch technology are researched, And the morphologyand reflectivity of the texture Surface are measured. The result shows that the optimaltechnology of the chemical acid etch is as follows: the composition and ratio of thechemical acid etching is HF:HNO₃:H₂O:CH₃COOH=1:6:3:1（volume ratio）; The etchingtime is300s; The etching temperature is5℃. The reflectivity of the multicrystallinesilicon texture surface is18.7%at400¹100nm wavelength.2) The paper proposes to apply second etching to prepare multicrystalline silicontexture Surface. The effect of different current density on the surface microscope ofmulticrystalline silicon is studied by the electrochemical etching in the HF:CH₃CH₂OH=1:2solution; then the surface loosed structure of the multicrystalline silicon isremoved through the chemical acid etching to form high performance surface texture.Surface microscope of multicrystalline silicon is characterized by the scanning electronmicroscopy, the results show that the surface porous structure of the multicrystallinesilicon is prepared after electrochemical etched300s while the favorable current densityis30mA/cm2; after ultransonic etched60s in the HF:H₂O₂=4:1chemical acid solutionat15℃the surface texture which hole diameter is2³Î¼m and hole depth is1.5³Î¼m is attained, the reflectivity of the multicrystalline silicon texture surface is16.4%at400¹100nm wavelength.3) The combination of optical mask technique with chemical etching technique areapplied to prepare multicrystalline silicon texture surface, which may improve theperformance of multicrystalline silicon texture surface. Firstly, the pattern of maskboard is copied to the positive photoresist on multicrystalline silicon surface bylithography technique, and then multicrystalline silicon is etched in chemical acidsolution to produce multicrystalline silicon uniform texture surface. The optimal etchprocess of multicrystalline silicon texture surface is as follows: the exposure time is9s;the imaging time is30s; the formulations etchant（HF: HNO₃: H₂O: CH₃COOH） is1:6:3:1; the etching time is90s. The reflectivity of the multicrystalline silicon texturesurface is11.0%at400¹100nm wavelength.On the basis of series of experiments, the texture surface of multicrystalline siliconby chemical acid etching may reduce the reflectivity of solar cells and is suitable for thesolar cell production process, however, the uncontrollability of etching process, and theuneven of texture surface is considered as factors limiting the performance and Thus,the electrochemical and optical mask techniques have been proposed which reducingthe acid etching time, increasing the controllability of the corrosion reaction andimproving the uniformity of the multicrystalline silicon texture surface.